Spectrally resolved UV absorption cross sections between 190 and 320 nm were measured in shock-heated CO2 between 880 and 3050 K and H2O between 1230 and 2860 K. Absorption spectra were acquired with 10 micro s time resoln. using a unique kinetic spectrograph, thereby enabling comparisons with time-dependent chem. kinetic modeling of post-shock thermal decompn. and chem. reactions. Although room temp. CO2 is transparent (s<10-22 cm2) at wavelengths longer than 200 nm, hot CO2 has significant absorption (s>10-20 cm2) extending to wavelengths longer than 300 nm. The temp. dependence of CO2 absorption strongly suggests sharply increased transition probabilities from excited vibrational levels.